From cppreference.com
boolvalid()constnoexcept;(since C++11)Checks if the future refers to a shared state.
This is the case only for futures that were not default-constructed or moved from. Unlike
, std::shared_future's shared state is not invalidated when get() is called.
The behavior is undefined if any member function other than the destructor, the copy-assignment operator, the move-assignment operator, or valid is called on a shared_future that does not refer to shared state (although implementations are encouraged to throw
indicating no_state in this case). It is valid to move or copy from a shared_future object for which valid() is false.
Parameters
(none)
Return value
true if *this refers to a shared state, otherwise false.
Example
Run this code
#include<future>#include<iostream>intmain(){std::promise<void>p;std::shared_future<void>f=p.get_future();std::cout<<std::boolalpha;std::cout<<f.valid()<<'\n';p.set_value();std::cout<<f.valid()<<'\n';f.get();std::cout<<f.valid()<<'\n';}Output:
true true true See also
waits for the result to become available
(public member function)